1. Field of the Invention
This invention relates to a method for forming a desired deposited film on a substrate by introducing starting gases into a vacuum chamber, giving an appropriate energy such as heat, gas plasma, light, etc., thereby causing the starting gases to undergo decomposition or other chemical reactions, particularly to a method for formation of a deposited film containing silicon.
2. Description of the Prior Art
In the prior art, as the method for forming a deposited film of amorphous silicon (hereinafter written as "a-Si"), there have been known the glow discharge deposition method, the heat energy deposition method or the light energy deposition method employing SiH.sub.4 or Si.sub.2 H.sub.6 as the starting gas.
However, in the deposited film containing silicon formed from the above starting gas, although there is a slight difference depending on the deposition method, Si--H bondings and Si--H.sub.2 bondings are contained in amounts on the same order, ad it has been impossible to obtain a deposited film containing selectively either one type of the bondings in greater amount.
On the other had, according to D. I. Wolford et al. (Appl. phys. Lett. 42(4), Feb. 15, 1983), in the deposited film formed by heating only the starting gas to high temperture, while maintaining the substrate at around room temperature, strong luminescence is observed in the visible region, suggesting strongly the relationship between its intensity, the defect density of the film measured by the electron spin resonance method and the amount of Si--H.sub.2 bondings contained in the film. For example, as Si--H.sub.2 bondings or --(Si--H.sub.2).sub.n --chains in the film are increased, the defect density will be reduced and the photoluminescence intensity will be increased.
Such a method of Wolford et al is a method in which the product substance through the reaction in gaseous phase is directly deposited on the substrate, while suppressing the reaction in the substrate by maintaining the substrate at a low temperature, whereby the amount of Si--H.sub.2 bondings in the film can be increased, but not to a satisfactory extent.
Thus, in the methods for forming deposited film of the prior art as described above, the amount of Si--H.sub.2 bondings which determine the quality of the deposited film could not satisfactorily be increased.